What happened
On May 6, 2021, an AS 350 B2 helicopter, registration PP-PIT, was conducting a local inspection of power transmission grids in the rural area of Arapoti, Paraná. The flight, operated by Helisul Air Taxi Ltd., included the pilot and three passengers.
While flying parallel to the transmission lines at a speed of 30 knots, the aircraft was positioned approximately 10 meters from a power tower to facilitate inspection by technicians on board. During this maneuver, a gust of wind caused the helicopter to drift toward the power cables, resulting in the main rotor blades striking a chain of insulators. Following the collision, the crew experienced intense vibrations in the controls and performed an emergency landing in a nearby open field. All four occupants escaped the aircraft unharmed, though the helicopter sustained substantial damage to its main rotor blades.
The investigation
CENIPA's investigation focused on the operational procedures and environmental factors during the low-altitude flight. Investigators found that the aircraft was within weight and balance limits and that all maintenance records were up to date. While weather conditions were generally favorable, the presence of wind gusts proved critical during the close-proximity maneuver.
The investigation also examined the operational guidelines being used. The crew was following a Technical Field Manual provided by the contracting company, Furnas Centrais Elétricas S.A. However, investigators noted that the aircraft was flying at a lateral distance of only 10 meters from the tower, whereas the manual's safety provisions recommended a distance of approximately 15 meters. This reduced margin of error decreased the pilot's response time when the wind gust occurred.
Findings
- Reduced safety margin: The decision to fly 10 meters from the tower, rather than the recommended 15 meters, increased the risk of collision.
- Wind interference: A gust of wind moved the aircraft into the path of the insulators, and the pilot was unable to avoid the impact.
- Outdated guidance: The technical manual used for the operation was considered outdated, as it did not account for modern technological advances, such as the high-resolution cameras used in the aircraft, which could allow for safer standoff distances.
- Training and planning: There was no evidence that the pilot had received specific training in mountain flying techniques, and the operator lacked a specific training program for transmission line inspections. Additionally, flight planning may not have sufficiently accounted for wind intensity near large obstacles.